Push buttons are widely used as inputting means of input devices employed in input operating sections of a variety of electronic apparatus. Portable phones are one of instances employing such input devices. Operating such an input device allows inputting telephone numbers.
In recent years, since the access to the Internet has become easier, users can browse the Internet web sites frequently through portable phones, so that the users need to move the cursor on display as they like. Unexamined Japanese Patent Publication No. 2002-123363 discloses an input device for the operation discussed above. This input device is formed by combining a coordinate input unit for moving a cursor on a display with a push-switch input unit for inputting telephone numbers. This conventional input device is described hereinafter with reference to FIG. 6.
FIG. 6 shows a sectional view in part of the conventional input device of which substrate 205 includes conductive units such as a given wiring. On the top surface of substrate 205, center electrode 201 and doughnut-like outer-rim electrode 202, which surrounds center electrode 201, are placed. These electrodes are coupled via through holes 203 to pattern 204 placed on the underside of substrate 205, so that they are led to the outside of the input device.
Diaphragm 206 is made of elastic thin metal plate and has a circular appearance. It forms a movable contact which is shaped like a dome bowing upward. Diaphragm 206 is placed on substrate 205 such that the lower end of its rim touches outer-rim electrode 202, and its top surface is covered with resin sheet 208 made from PET (polyethylene terephthalate). Resin sheet 208 includes adhesive member 207 on its underside. Adhesive member 207 adhesively holds the top surface of diaphragm 206. Adhesive member 207 on the surroundings of diaphragm 206 is stuck to the top surface of substrate 205, so that diaphragm 206 is fixed to and positioned at substrate 205.
Above resin sheet 208 that covers diaphragm 206, coordinate input sheet 209 is placed with a given space in between. Sheet 209 is formed of resin film having a given conductive pattern and integrated with display sheet 211 that is formed on sheet 209 and made of rubber. Although it is not illustrated in the drawings, coordinate input sheet 209 and display sheet 211 integrated with each other are supported at their outer circumferences by a housing of the apparatus so as not to be loosened.
The section of display sheet 211 placed just above diaphragm 206 forms display section 210 slightly rising in sheet 211, and display section 210 has a letter or number displayed on its top surface. The elements discussed above form a part of the conventional input device, and they are placed on a back-to-back basis in, e.g. a portable phone.
Operation of this conventional input device is described hereinafter. Display section 210 having a letter or a number thereon is pushed with a finger, then display sheet 211 bows downward with display section 210 as a center while the circumference of sheet 211 is stretched. Coordinate input sheet 209 also bows downward accordingly until it touches resin sheet 208 that fixes diaphragm 206 to substrate 205.
Further pushing display section 210 turns the center part of diaphragm 206 inside out, i.e. the center part bows downward, and this inside-out movement gives a tactile click impression to a user. Then the underside of the center part touches center electrode 201, which becomes conductive with outer-rim electrode 202 of substrate 205 via diaphragm 206. In other words, respective patterns 204 led to the underside of substrate 205 become shorted.
In this state, the finger is left from display section 210, namely, the pushing force on display section 210 is removed, then diaphragm 206 is restored to its original upwardly bowing domed posture by its own restoring force. This restoring movement of diaphragm 206 upwardly pushes coordinate input sheet 209 and display sheet 211, so that the postures of these elements are restored to the original ones shown in FIG. 6, i.e. the postures taken before the push operation.
A status when a coordinate is input is briefly described hereinafter. Inputting a coordinate is done by touching display sheet 211 with a finger. Since the fingers are conductive, the electrostatic capacity of coordinate input sheet 209 varies depending on the position of the finger touching on sheet 211. The conventional input device detects a coordinate position in the following way: a change in the electrostatic capacity due to a movement of the finger is input from sheet 209 to a controller (not shown) capable of calculating the coordinate position, and the controller processes this input in a given way.
However, since the conventional input device has display sheet 211 made of rubber (elastic material) and coordinate input sheet 209 made from resin film, a touch on display sheet 211 with a finger incurs downward bow of sheet 211. As a result, an interval between coordinate input sheet 209 and the conductive units provided to substrate 205 is changed. This change invites another change in the electrostatic capacity of coordinate input sheet 209. This another change is added to the change, which varies depending on the finger position, in the electrostatic capacity of sheet 209. As a result, an accuracy of detecting a coordinate position based on the change in the electrostatic capacity is lowered.
At the input operation, i.e. pushing display section 210 which has a letter or number thereon, since display sheet 211 is apart from diaphragm 206, the operation sometimes gives an unsteady impression to an operator. A slant pushing on display section 210 pushes it down in the slant direction, so that this push hits a point out of the center of diaphragm 206. As a result, a poor tactile click impression is given to the operator.